Dozens of foreign dignitaries including former US President Bill Clinton, Turkish Prime Minister Ahmet Davutoglu , Britain's Princess Anne and Jordan's Queen Noor were also coming for a ceremony mourning the 8,000 Muslim men and boys killed in the eastern Bosnian town of Srebrenica by Bosnian Serb troops.
The crime was later defined as genocide by two international courts.
Families will lay the remains of 136 victims to rest at a memorial center next to the graves of over 6,000 previously found in mass graves.
Some 15,000 men tried to flee through the woods toward government-held territory while others joined the town's women and children in seeking refuge at the base of the Dutch U.N. troops.
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The outnumbered Dutch troops could only watch as Serb soldiers rounded up about 2,000 men for killing and later hunted down and killed another 6,000 men in the woods.
So far, remains of some 7,000 victims have been excavated from 93 graves or collected from 314 surface locations and identified through DNA technology. None of the 136 bodies to be laid to rest Saturday are complete.
This week, a proposed UN Security Council over a resolution that called the crime "an act of genocide" was vetoed by Russia. In return, Srebrenica organisers withdrew an invitation to the Russian ambassador for Saturday's ceremony.
For three days, nearly 10,000 people retraced in reverse the march taken by those fleeing Srebrenica men and arrived Friday evening, in time to help families carry the 136 coffins from the former UN base, across the road to the memorial center.